The Program centers on clarifying respiratory mechanisms and their control during the development of the individual organism. All components of prenatal oxygen supply are under study: maternal, placental, and fetal. The transition to lung breathing at birth is also of particular interest. Since initial funding of the Program on June 1, 1976 (1 1/2 years ago) the following studies have been productive: maternal and fetal responses to maternal exercise; chemistry and function of uterine renin; placental transfer mechanisms for O2 and solutes; development of the avian embryo in different incubator environments; distribution of fetal cardiac output; fetal water balance and its control; and effects on mother and newborn of methadone addiction. Projects to study the control of fetal breathing and changes in blood oxygen transport following birth have been added. Core facilities for blood gas analysis, data processing, animal care and radioactive storage and monitoring are operative. This supplement requests funds to strength the core facilities, to explore the effects of ventilation in utero, to study the kinetics of placental glucose transport, to investigate the respiratory effects of female sex hormones and to evaluate respiratory control in infants with evidence of hypoventilation.